Three-dimensional porous polyurea networks and methods of manufacture

ABSTRACT

Porous three-dimensional networks of polyurea and porous three-dimensional networks of carbon and methods of their manufacture are described. In an example, polyurea aerogels are prepared by mixing an triisocyanate with water and a triethylamine to form a sol-gel material and supercritically drying the sol-gel material to form the polyurea aerogel. Subjecting the polyurea aerogel to a step of pyrolysis may result in a three dimensional network having a carbon skeleton, yielding a carbon aerogel. The density and morphology of polyurea aerogels can be controlled by varying the amount of isocyanate monomer in the initial reaction mixture. A lower density in the aerogel gives rise to a fibrous morphology, whereas a greater density in the aerogel results in a particulate morphology. Polyurea aerogels described herein may also exhibit a reduced flammability.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/375,757, filed Aug. 20, 2011, entitled“Three-Dimensional Porous Polyurea Networks and Methods of Manufacture,”by Leventis et al.

FEDERALLY SPONSORED RESEARCH

Research leading to various aspects of embodiments presented herein weresponsored, at least in part, by the National Science Foundation, GrantNo. CHE-0809562, Grant No. CMMI-0653919 and Grant No. CMMI-0653970. TheUnited States Government may have certain rights in the invention.

BACKGROUND

1. Field

Aspects herein relate to three-dimensional porous polyurea networks,three-dimensional porous carbon networks, uses thereof, and methods ofmanufacture.

2. Discussion of Related Art

Three-dimensional porous architectures are a desirable form factor formany materials as they allow installation of new properties into amaterial not possessed by the non-porous form of a material. Porousarchitectures possessing nanostructured features, such as nanopores ornanoparticulate solid frameworks, are further desirable in many cases asthey can possess new and/or more extreme properties than porousarchitectures without nanostructured features.

Aerogels are an example of a porous architecture possessingnanostructured features. Aerogels are materials comprised ofthree-dimensional assemblies of densities Aerogel materials aretypically produced by forming a gel that includes a porous solidcomponent and a liquid component and then removing the liquid componentby supercritically, subcritically, or freeze drying the wet gel toisolate the porous solid component. This porous solid component is anaerogel. Supercritical drying involves the liquid being transformed intoa fluid above its critical point and removing the fluid while leavingthe porous solid structure generally intact. Subcritical drying involvesevaporation of the liquid below its critical point in a way that leavesthe porous solid structure generally in tact. Freeze drying involvesfreezing of the liquid component and sublimation of the resulting solidin a way that leaves the porous solid structure generally in tact.

The large internal void space in aerogels and other nanostructured andnon-nanostructured three-dimensional porous networks generally providesfor a low dielectric constant, a low thermal conductivity, and a highacoustic impedance. These materials have been considered for a number ofapplications including thermal insulation, lightweight structures, andimpact resistance.

SUMMARY

Articles and methods for manufacturing three-dimensional porous polyureanetworks and three-dimensional porous carbon networks are described.

Polyurea aerogels can be prepared by mixing an isocyanate with water anda trialkylamine in forming a sol-gel material and subsequently dryingthe sol-gel material to form the polyurea aerogel. The sol-gel materialmay be dried supercritically or subcritically. The density of polyureaaerogels can be tailored by controlling the concentration of isocyanatein the initial mixture. For example, increasing the amount of isocyanatein forming the sol-gel material may give rise to a polyurea aerogelhaving an increased density. Conversely, decreasing the amount ofisocyanate in forming the sol-gel material may give rise to a polyureaaerogel having a lower density. The morphology of polyurea aerogels canalso be tailored by controlling the amount of isocyanate in thecomposition during manufacture. Including a low amount of isocyanate inthe initial mixture to form the sol-gel material may give rise to apolyurea aerogel having a fibrous morphology. Also, having an increasedamount of isocyanate in the initial mixture to form the sol-gel materialmay give rise to a polyurea aerogel having a particulate morphology. Insome cases, a polyurea aerogel may have a fibrous morphology which mayor may not include features of a particulate morphology when the densityof the aerogel is less than about 200 mg/cc. Further, polyurea aerogelsmay exhibit reduced flammability characteristics, for example, whenhaving a density of greater than about 150 mg/cc.

Carbon aerogels may also be manufactured from polyurea aerogels througha conversion step. Once a polyurea aerogel is formed, the aerogel may besubject to a pyrolysis step, giving rise to a carbon skeleton in theaerogel, hence, forming the carbon aerogel. In some embodiments, apolyurea aerogel having a fibrous morphology that is subject to thepyrolysis step may give rise to a carbon aerogel also having a fibrousmorphology. In some cases, carbon aerogels having a fibrous morphologymay have a density of less than about 150 mg/cc.

In some cases, three-dimensional porous polyurea networks not consideredaerogels may be produced. Likewise, three-dimensional porous carbonnetworks not considered aerogels may be derived from suchthree-dimensional polyurea networks.

Various embodiments of the present invention provide certain advantages.Not all embodiments of the invention share the same advantages and thosethat do may not share them under all circumstances.

Further features and advantages of the present invention, as well as thestructure of various embodiments of the present invention are describedin detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Forpurposes of clarity, not every component may be labeled in everydrawing. Various embodiments of the invention are described, by way ofexample, in the accompanying drawings. In the drawings:

FIG. 1 shows a plurality of isocyanate reactions in accordance with someembodiments;

FIG. 2 shows a plurality of isocyanate precursors in accordance withsome embodiments;

FIG. 3 depicts a reaction resulting in a polyurea aerogel in accordancewith some embodiments;

FIG. 4 a shows a scanning electron microscope (SEM) image of silicananoparticles prior to application of a conformal coating;

FIG. 4 b illustrates a schematic representation of silica in accordancewith some embodiments;

FIG. 5 a shows an SEM image of silica nanoparticles having a conformalcoating applied;

FIG. 5 b illustrates a schematic representation of silica nanoparticleshaving a conformal coating applied;

FIG. 6 depicts a schematic representation of a reaction wherereinforcement is applied to interparticle necks of silica nanoparticlesin accordance with some embodiments;

FIG. 7 shows a flow chart of the preparation of a polyurea aerogel inaccordance with some embodiments;

FIG. 8 shows another flow chart of the preparation of a polyurea aerogelin accordance with some embodiments;

FIG. 9 depicts a system used for preparation of a polyurea aerogel andthe results obtained in the preparation in accordance with someembodiments;

FIG. 10 illustrates a schematic representation of a system for preparingdensity-gradient polyurea wet gels in accordance with some embodiments;

FIG. 11 shows gelation time data of a polyurea aerogel prepared withDesmodur N3300A in accordance with some embodiments;

FIG. 12 shows more gelation time data of a polyurea aerogel preparedwith Desmodur N3300A in accordance with some embodiments;

FIG. 13 a depicts a graph of percent concentration of catalyst andequivalence of water as a function of gelation time of a polyureaaerogel in accordance with some embodiments;

FIG. 13 b shows a graph of bulk density and percent porosity as afunction of concentration of monomer in accordance with someembodiments;

FIG. 14 a depicts a graph of bulk density and percent linear shrinkageas a function of concentration of N3300A in the sol in accordance withsome embodiments;

FIG. 14 b illustrates a graph of percent porosity as a function ofpercent bulk density in accordance with some embodiments;

FIG. 15 a shows nuclear magnetic resonance (NMR) spectra of a polyureaaerogel and desmodur N3300A in accordance with some embodiments;

FIG. 15 b illustrates infrared (IR) spectra of a polyurea aerogel anddesmodur N3300A in accordance with some embodiments;

FIG. 16 depicts x-ray diffraction (XRD) data of polyurea aerogelsexhibiting increasing crystallinity with increasing density inaccordance with some embodiments;

FIG. 17 depicts XRD data of polyurea aerogels prepared in accordancewith some embodiments;

FIG. 18 a shows a SEM image of a low density polyurea aerogel inaccordance with some embodiments;

FIG. 18 b shows a SEM image of a high density polyurea aerogel inaccordance with some embodiments;

FIG. 19 depicts SEM images of polyurea aerogels under a constantconcentration of N3300A at different gelation times in accordance withsome embodiments;

FIG. 20 shows SEM images, nitrogen sorption isotherms and BJH desorptionplots of polyurea aerogels in accordance with some embodiments;

FIG. 21 also shows SEM images, nitrogen sorption isotherms and BJHdesorption plots of polyurea aerogels in accordance with someembodiments;

FIG. 22 illustrates SEM images of polyurea aerogels prepared inaccordance with some embodiments;

FIG. 23 depicts more SEM images of polyurea aerogels prepared inaccordance with some embodiments;

FIG. 24 shows SEM images of a high density portion of a polyurea aerogelin accordance with some embodiments;

FIG. 25 depicts SEM images of a low density portion of a polyureaaerogel in accordance with some embodiments;

FIG. 26 depicts a stress-strain graph, SEM images and photographs of apolyurea aerogel in accordance with some embodiments;

FIG. 27 illustrates a stress-strain graph of a high density polyureaaerogel in accordance with some embodiments;

FIGS. 28 a-28 c show polyurea aerogels exhibiting various degrees offlame retardancy in accordance with some embodiments;

FIG. 29 a illustrates SEM images of a polyurea aerogel converted to acarbon aerogel and a graph of percent weight as a function oftemperature in air and nitrogen in accordance with some embodiments;

FIG. 29 b depicts SEM images of another polyurea aerogel converted to acarbon aerogel and a graph of percent weight as a function oftemperature in air and nitrogen in accordance with some embodiments;

FIG. 30 a illustrates XRD data of carbon obtained from a polyureaaerogel in accordance with some embodiments;

FIG. 30 b shows raman spectrua of carbon obtained from a polyureaaerogel in accordance with some embodiments;

FIG. 31 illustrates a solids CPMAS ¹³C NMR spectra of (A) a high-densitypolyurea aerogel made of Desmodur RE triisocyanate, (B) a low-densitypolyurea aerogel made of Desmodur RE triisocyanate, and (C) a liquids¹³C NMR spectra of the monomer in CDCl₃;

FIG. 32 depicts a solids CPMAS ¹³C NMR of (A) a high-density polyureaaerogel made of Desmodur N3200 diisocyanate, (B) a low-density polyureaaerogel made of Desmodur N3200 diisocyanate, and (C) a liquids ¹³C NMRspectra of the monomer in CDCl₃; and

FIG. 33 shows an example of a polyurea aerogel used to absorb crude oilin accordance with some embodiments.

DETAILED DESCRIPTION

Aspects described relate to three-dimensional polyurea networksincluding polyurea aerogels and methods of manufacturingthree-dimensional porous polyurea networks.

A polyurea aerogel may be prepared by mixing an isocyanate reactant,such as diisocyanate or triisocyanate, with water and a trialkylamine(e.g., trimethylamine, triethylamine, tributylamine) in a solvent (e.g.,acetone, DMSO) to form a sol-gel material including polyurea. Thesol-gel material may subsequently be dried supercritically,subcritically, or by freeze drying to form a polyurea aerogel. Mixtureof a diisocyanate or triisocyanate reactant with water and atrialkylamine results in in-situ amine formation which reacts furtherwith unreacted isocyanate to form polyurea. A number of characteristics,such as density, nanomorphology, porosity, pore size, surface area,flammability, and mechanical strength can be controlled by the chemicalidentity and concentration of the isocyanate.

Polyurea aerogels of the present invention may exhibit certaincharacteristics, for example, related to various degrees of density,morphology and flammability. In some embodiments, the density of thepolyurea aerogel is controlled by varying amounts of di- ortriisocyanate prepared in an initial manufacturing step. The morphologyof the polyurea aerogel may also be controlled. In some embodiments, forexample, a polyurea aerogel exhibits a fibrous morphology. In otherembodiments, a polyurea aerogel has a particulate ball-like morphology.In some cases, the morphology of a polyurea aerogel relates to thedensity of the polyurea aerogel. Morphologies of a polyurea aerogel canbe tailored according to usage of varying amounts of di- ortriisocyanate during manufacture of the polyurea aerogel. In someembodiments, polyurea aerogels manufactured exhibit high mechanicalstrength properties and are generally not flammable or exhibit lowflammability.

Porous polyisocyanate-based organic networks can be prepared by mixingan organic polyisocyanate and an isocyanate trimerization catalyst,1,4-diazobicyclo[2.2.2]octane (DABCO), to form a polymeric gel andsupercritically drying the gel to produce a polyisocyanate-basedaerogel. Such aerogels and their methods of manufacture are described inU.S. Pat. No. 5,484,818 entitled “Organic aerogels,” and is incorporatedherein by reference in its entirety. Polyurea aerogels described hereinare prepared via in situ formation of amines by reaction of isocyanateswith water where the density, nanomorphology, porosity, pore size,surface area, flammability, and mechanical strength can be suitablytuned.

Aspects described herein may also relate to three-dimensional porouscarbon networks including aerogels and methods of manufacturingthree-dimensional porous carbon networks. In manufacturing athree-dimensional porous carbon network, a three-dimensional porouspolyurea network may be prepared as a precursor to the three-dimensionalporous carbon network. For example, in manufacturing a carbon aerogel, apolyurea aerogel may be prepared as a precursor to the carbon aerogel.As discussed, in some embodiments, the polyurea aerogel may be preparedby mixing a diisocyanate or a triisocyanate reactant with water and atrialkylamine and subjecting the mixture to agitation to form a sol-gelmaterial. Then, the sol-gel material is supercritically, subcritically,or freeze dried, resulting in the polyurea aerogel. Once formed, thepolyurea aerogel is then pyrolyzed to form a carbon aerogel. In someembodiments, carbon aerogels may have electrically conductiveproperties.

Once pyrolyzed, three-dimensional porous carbon networks may retain thesame or similar morphology as the polyurea precursor. Accordingly, insome embodiments, carbon aerogels produced from polyurea aerogels havinga fibrous morphology by methods described herein may also exhibit afibrous morphology. In other embodiments, carbon aerogels prepared frompyrolysis of polyurea aerogels having a particulate morphology may alsohave a particulate morphology.

In some embodiments, polyurea or carbon aerogels of different densitiesmay be prepared by varying the concentration of triisocyanate (e.g.,Desmodur N3300A), or diisocyanate, in the sol-gel material. In someembodiments, the density of polyurea aerogels or carbon aerogelsprepared from pyrolysis of polyurea aerogels may be between, forexample, about 1 mg/cc and about 550 mg/cc, or between about 15 mg/ccand about 500 mg/cc. In some embodiments, the density of polyureaaerogels or carbon aerogels prepared from pyrolysis of polyurea aerogelsmay be less than about 900 mg/cc, less than about 500 mg/cc, less thanabout 150 mg/cc, less than about 90 mg/cc, less than about 10 mg/cc, orless than about 1 mg/cc. Previously, it had been challenging to produceopen-pore mesoporous materials at a low density that are durable andmade from inexpensive chemicals and recyclable solvents. Aerogelspresented herein include an open-cell mesoporous foam that is notfragile and remains durable at densities as low as 0.04 g/cc. Bycomparison, silica aerogels at such low density may exhibit extremelyfragile mechanical properties.

The density of polyurea or carbon aerogels prepared in accordance withmethods described may be appropriately tailored based on theconcentration of isocyanate material included in the initial mixture.For example, when preparing a polyurea or carbon aerogel, including moreisocyanate material in the initial mixture may give rise to a polyureaor carbon aerogel having a greater density. Similarly, including lessisocyanate material in the initial mixture during preparation of apolyurea or carbon aerogel may result in a polyurea or carbon aerogelhaving less density.

The morphology of aerogels described herein may be appropriatelycontrolled. In some embodiments, the morphology of a polyurea or carbonaerogel may be controlled based on the amount of isocyanate incorporatedinto the initial mixture of isocyanate, water and trialkylamine. In somecases, for example, a suitable mixture having a smaller amount ofisocyanate in forming a sol-gel material, upon drying of the sol-gelmaterial, may give rise to a polyurea aerogel or carbon aerogel (afterpyrolysis) having a more fibrous morphology as compared to an aerogelhaving been prepared from a similar mixture yet having a larger amountof isocyanate. On the other hand, a suitable mixture having a largeramount of isocyanate, when the sol-gel material is appropriately formedand dried, may result in a more particulate-type morphology as comparedto an aerogel prepared from a similar mixture that includes a largeramount of isocyanate. Low-density polyurea and carbon aerogels mayexhibit fibrous morphology, whereas high-density polyurea and carbonaerogels may show a particulate morphology.

Aerogels discussed herein may have fibrous morphologies where theaerogels may include nanofibers having various diameters and lengths. Insome embodiments, fibrous morphologies of aerogels include fibers havingan average diameter ranging between about 1 nm and about 500 nm (e.g.,between about 10 nm and about 400 nm, between about 100 nm and about 300nm) or less than 500 nm (e.g., less than 400 nm, less than 300 nm, lessthan 200 nm). In some embodiments, fibrous morphologies of aerogelsinclude fibers having an average length of at least 50 nm and may extendinto the micron length scale.

Polyurea aerogels discussed herein may have advantageous mechanicalstrength properties. In some embodiments, the compressive strength ofpolyurea aerogels may be between about 200 MPa and about 1 GPa, betweenabout 400 MPa and about 800 MPa, or between about 600 MPa and about 700MPa (e.g., at least 640 MPa). The specific energy, as calculated by thearea under a compressive stress-strain curve, can be between about 10J/g and about 200 J/g, between about 50 J/g and about 150 J/g, orbetween about 80 J/g and about 120 J/g (e.g., at least 105 J/g).

Three-dimensional porous polyurea networks having a certain densitylevel may exhibit flame retardancy properties. In some embodiments, by aflame test, low-density polyurea aerogels were found to burn completely,but high-density polyurea aerogels did not sustain a flame. In somecases, low density polyurea aerogels burn completely but high densitypolyurea aerogels do not sustain a flame. For example, as shown in FIGS.28 a-28 c, a variable-density polyurea aerogel will ignite at alow-density end and the flame will propagate until it approaches ahigh-density region, where the flame will then self-extinguish. In someembodiments, polyurea aerogels may exhibit significantly reducedflammability characteristics at densities above about 150 mg/cc. Forexample, a flame will not survive at regions of a polyurea aerogel wherethe density is greater than about 150 mg/cc. In some cases, ahigh-density polyurea aerogel may exhibit a more particular morphology(less fibrous) and, hence, may have less surface area for which a flamemay be sustained.

Isocyanate (N═C═O) is a reactive functional group and may undergoreaction with a number of nucleophiles. FIG. 1 shows several examples ofreactions which may involve isocyanates. Generally, an in-situ amineformed by the reaction of isocyanate with water reacts with isocyanateto yield a urea molecule. Such a reaction may be useful for preparingporous polyurea materials (e.g., aerogels) described herein.

Any appropriate diisocyanate, triisocyanate, or any other isocyanate,may be used as a monomer in forming a three-dimensional porous polyureanetwork such as a polyurea aerogel. Examples of suitable, yet notlimiting, diisocyanate monomers include Desmodur N3200 diisocyanate,toluene diisocyanate (Mondur TDS), and MDI (Mondur CD). Examples ofsuitable, yet not limiting, triisocyanate monomers include DesmodurN3300A triisocyanate and Desmodur RE triisocyanate. FIG. 2 illustratesexamples of isocyanates, such as Desmodur RE (TMT), Desmodur N3300A andDesmodur N3200 (e.g., may be obtained from Bayer Corp.), which may beused as precursors for the preparation of three-dimensional porouspolyurea networks (e.g., aerogels). FIG. 3 depicts an example reactionfor the preparation of a polyurea aerogel from Desmodur N3300A.

In some embodiments, polyurea aerogels are obtained upon base-catalyzedcrosslinking of resorcinol-formaldehyde (RF) wet gels withtriisocyanates. The outer surface layer of the porous solid component ofthe gel may include polyurea formed via an Et₃N-catalyzed reaction oftriisocyanate with residual water in an acetone or acetonitrilecrosslinking bath.

In some embodiments, aerogels are made by reaction of a triisocyanatesuch as Desmodur N3300A with water in the presence of a catalyst, suchas triethylamine in an acetone or acetonitrile solvent. The density andmicroscopic morphology exhibited by the resulting aerogel may becorrelated to the amount of triisocyanate, water, and catalyst utilizedin the manufacturing process. In some cases, triisocyanate may be usefulas monomers to produce lower density aerogels exhibiting fibrousmorphology. Such a result may be due to early phase separation due tolow solubility of the three-dimensional polymer arising from thetriisocyanate.

In various embodiments, the concentration of catalyst (e.g., Et₃N), theconcentration of monomer and the concentration of water may be varied toaffect different characteristics of polyurea aerogels. For example, tobe discussed further below, including an increasing amount of monomer(e.g., isocyanate) will result in a polyurea aerogel having a generallyincreased bulk density and a decreased percent porosity. Further, insome cases, increasing the amount of catalyst (e.g., Et₃N) and water maydecrease the overall gelation time of the aerogel. In some cases,varying the concentration of water and trialkylamine added in preparingpolyurea aerogels may have an effect on the gelation time, yet no effecton the nanomorphology of the resulting aerogels. However, in someembodiments, varying the concentration of monomer (di- or triisocyanate)may have a direct effect on both the gelation time and thenanomorphology of polyurea aerogels.

Polyureas may result from the reaction of isocyanates withmultifunctional nucleophiles such as polyamines. In a similar vein,polyurethanes may result from the reaction of isocyanates withmultifunctional nucleophiles such as polyols. High-surface-areapolyurethanes as the stationary phase for chromatographic separationsmay be formed via reaction in CH₂Cl₂ of polymeric methylene diphenyldiisocyanate (MDI, e.g., Mondur MR) and a pentafunctional oligomer basedon oxypropylation of diethylenetriamine. Such materials are obtained asprecipitates rather than gels, however, use of sugar derivatives aspolyols and more polar solvents for the reaction medium may yield gelsand eventually aerogels. For example, toluene diisocyanate may be usedto crosslink and induce pyridine-catalyzed gelation of cellulose acetateand cellulose acetate butyrate acetone solutions. Wet gels may be driedto aerogels with SCF CO₂.

In forming gels used in thermal superinsulation applications, aDABCO-catalyzed reaction in DMSO/ethyl acetate mixtures of an MDIderivative (e.g., Lupranat M205, a BASF product similar to Suprasec DNRby ICI) with saccharose and pentaerythritol may give rise tonanoparticulate polyurethane aerogels where the macro- vs. themesoporosity are controlled by adjusting the Hildebrand solubilityparameter via the DMSO/ethylacetate ratio. Aerogels having lower thermalconductivities than standard polyurethane foams may be formed (0.022 vs.0.030 W m⁻¹ K⁻¹, respectively, at room temperature and atmosphericpressure and comparable bulk densities of ˜0.2 g cm⁻³). Further,crosslinking of cellulose acetate in acetone with Lupranat M20Sisocyanate and dibutyltin laurate as a catalyst results in aerogels thatinclude a natural cellulose product, demonstrating high elastic moduli(in the 200-300 MPa range at bulk densities ρ_(b) in the range 0.75-0.85g cm⁻³) and low thermal conductivities ranging from 0.029 W m⁻¹ K⁻¹ (atatmospheric pressure) to 0.006 W m⁻¹ K⁻¹ (at 2×10⁻⁵ mbar) for sampleswith ρ_(b) of 0.25 g cm⁻³.

In some embodiments, polyurea aerogels may be synthesized in acetone viaEt₃N-catalyzed reaction of MDI or polymeric MDI type of isocyanates andtriamines. Polyurethane aerogels may be made from similar or the sameisocyanates and an ethylene oxide modified polyether polyol (e.g.,Multranol 9185). Polyurea aerogels may be nanoparticulate like silicaand polyurethane aerogels may be nanofibrous. For various densities(e.g., 0.12-0.13 g cm⁻³), polyurea aerogels may demonstrate lowerthermal conductivities than polyurethane aerogels (0.018-0.019 W m⁻¹K⁻¹, vs. 0.02+7 W m⁻¹K⁻¹, respectively). Both polyurea and polyurethaneaerogels, however, may exhibit higher thermal conductivity and densityvalues than that of silica aerogels (0.012 W m⁻¹ K⁻¹) at 0.09 g cm⁻³.

Polyureas may also be obtained indirectly from isocyanates and water viaa reaction sequence that initially yields an amine via an unstablecarbamic acid, shown in Reaction (1).

Subsequently, the amine reacts with yet-unreacted isocyanate yieldingurea (eq 2).

In some instances, Reaction (2) takes place much faster than Reaction(1), because amines are stronger nucleophiles than water. The seq/uenceof Reactions (1) and (2) may be used for the environmental curing offilms containing unreacted isocyanate groups, while, owing to the CO₂side product generated by the reaction, such reactions may also beinvolved in the formation of polyurethane foams w/here a small amount ofwater added in the reaction mixture acts as a foaming agent.

Synthesis of mechanically strong polyurea aerogels via reaction ofisocyanates with water, which had not previously been reported before,may be advantageous in that it bypasses the use of expensive amines. Insome embodiments, the gelation process may be employed withtriisocyanates such as Desmodur N3300A or Desmodur RE yielding polyureamonoliths over a wide density range (e.g., 0.016-0.55 g cm⁻³).Diisocyanates such as Desmodur N3200, toluene diisocyanate (TDI), ormonomeric MDI may also gel at higher concentrations. In some instances,however, polyurea aerogels produced from triisocyanates may exhibit morerobust characteristics than polyurea aerogels prepared fromdiisocyanates.

Aerogels derived from triisocyanates such as Desmodur N3300A may notonly exhibit variable nanomorphologies that are tunable as a function ofdensity, but such aerogels may also exhibit exceptional mechanicalproperties which are comparable to those of x-aerogels. X-aerogels,methods of manufacture, and their use are described in U.S. Pat. No.7,771,609 entitled “Methods and Compositions for Preparing SilicaAerogels” and is incorporated herein by reference by its entirety.

FIGS. 4 a and 4 b respectively depict a SEM image and a schematicrepresentation of an example of silica nanoparticles connected togetherprior to cross-linking of the silica nanoparticles, that is, prior toapplication of a conformal coating to the nanoparticles. Poroussecondary particles having a diameter of between about 5-10 nm are madeup of nonporous primary particles having a diameter of less than about 1nm. While the primary particles are arranged in a manner that formsmicropores within the secondary particles, larger mesopores arisethrough the arrangement of secondary particles relative to one another.In the example shown in FIG. 4 a, before cross-linking takes place, thedensity of the composition was measured to be approximately 0.18 g/cc.FIG. 4 b illustrates a silica nanoparticle network in the form of anaerogel that includes mesopores having voids that are between 2-50 nm indiameter between secondary particles. Primary particles include voidsthat are less than 2 nm in diameter.

FIGS. 5 a and 5 b respectively show a SEM image and a schematicrepresentation of cross-linked silica nanoparticles having a conformalcoating applied on to surfaces of the silica nanoparticles. Aftercross-linking of the nanoparticles, the conformal coating effectivelycovers the micropores between primary particles and within secondaryparticles. Additionally, the conformal coating forms thick necks betweensecondary particles, giving rise to an increased overall mechanicalstrength. In the example shown in FIG. 5 a, after cross-linking, thedensity of the composition was measured to be approximately 0.45 g/cc.In some embodiments, as illustrated in the schematic representation ofFIG. 6, upon application of an isocyanate (e.g., diisocyanate,triisocyanate), the interparticle necks 10 are reinforced with polyureatethers 20, resulting in a general strengthening of the overallcomposition.

Aerogels derived from triisocyanates such as Desmodur RE may provide fora high-yield conversion to carbon aerogels. Carbon aerogels derived fromdiisocyanates such as Desmodur N3200 may also be produced.

As discussed further below, such materials may exhibit a significantdegree of versatility and multifunctionality. For example, aerogelshaving density-gradient monoliths may include a high-densitynanoparticulate end that combines high mechanical strength with flameretardancy.

FIGS. 7 and 8 illustrates examples of suitable steps that may be used toprepare various polyurea aerogels, the steps being described below.Polyurea aerogels of different densities may be prepared by varying theconcentration of the monomer in the initial mixture for forming theaerogel. In some embodiments, a diisocyanate or triisocyanate monomer isdissolved in a suitable solvent, such as acetone or DMSO. An appropriateamount of water is subsequently added and a sol-like material is formedby adding a trialkylamine to the mixture. Any suitable trialkylamine maybe used, such as for example, trimethylamine, triethylamine,tributylamine, tripentylamine, and so on. The mixture may be agitated(e.g., shaken vigorously, sonicated, mixed) to form a gel and allowed toset in a mold for an appropriate gelation time. Gelation times may vary,for example, between 5 minutes and 24 hours. Gelation times may dependon the concentration of the monomer, water and the catalyst. Generally,gelation times will be lower at higher concentrations of all threematerials. As a note, previous reports had not considered use of waterin forming a polyurea aerogel. As a further note, previous reports hadnot been able to induce a fibrous morphology in polyurea aerogel, norcontrol its flammability.

After allowed to age, gels are removed from their molds and subject to aprocess of solvent exchange. In some embodiments, solvent exchangeinvolves contacting or immersing the gel in an aprotic solvent, such asfor example, acetone, pentane, or acetonitrile. Such solvents may enablethe formation of CO₂-containing voids in the overall composition.However, it can be appreciated that any suitable solvent may beutilized. Solvent exchange may be performed a number of times prior todrying of the sol-gel, for example, with supercritical CO₂ to form anaerogel. In some cases, the gel may be dried at an elevated temperature(e.g., 40° C.) under ambient pressure. In some embodiments,supercritical drying is conducted in an autoclave where the temperatureof the autoclave is raised above the critical point of CO₂ and thepressure is released isothermally (e.g., at 40° C.). In otherembodiments, subcritical drying is used to dry the sol-gel material,forming the aerogel.

In some embodiments, and as shown in FIGS. 9 and 10, variable densitypolyurea aerogels may be synthesized by beginning to fill a mold with ahigh concentration of sol using an appropriate pump and constantlydiluting the sample with a low concentration sol using a second pump. Asshown in FIG. 8, high density sol (e.g., initially 0.2969 M) is pumpedcontinuously from container B to container C. However, low density sol(e.g., 0.1084 M) is simultaneously being pumped from container A tocontainer B so as to dilute the composition in container B. As a result,the resulting sol-like material in container C may became hazy andgelled progressively from one end to the other (e.g., from the bottomup). The illustrations at the bottom of FIG. 9 both show a gradient indensity and transmittance (mean ROI intensity) from one end of the gelto the opposite end.

Further, and as discussed, carbon aerogels may be produced by subjectingpolyurea aerogels described herein to an additional step of pyrolysis.In some embodiments, a polyurea aerogel is placed in an inert atmosphere(e.g., Ar) at a high temperature (e.g., 800° C.), yielding an aerogelhaving a carbon skeleton. In some embodiments, the skeleton of thecarbon aerogel is made of purely carbon material. In some embodiments,carbon aerogels formed by methods discussed may exhibit a fibrousmorphology. For example, pyrolyzing a polyurea aerogel having a fibrousmorphology (e.g., low-density) may result in a carbon aerogel alsohaving a fibrous morphology. Depending on various parameters, carbonaerogels may exhibit a particulate morphology. For example, pyrolyzing apolyurea aerogel having a particulate morphology (e.g., high-density)may give rise to a carbon aerogel that has a similar particulatemorphology. Carbon aerogels may also contain electrically conductivecharacteristics.

Three-dimensional porous polyurea and carbon networks (e.g., aerogels)discussed may be suitable for use in a number of applications. Aerogelsmay generally be used for applications including thermal insulation(e.g., architectural, automotive industrial applications, aircraft,spacecraft, clothing), acoustic insulation (e.g., buildings,automobiles, aircrafts), dielectrics (e.g., for fast electronics),supports for catalysts, and as hosts of functional guests for chemical,electronic and optical applications. In some cases, three-dimensionalporous polyurea networks including polyurea aerogels may be useful forapplications that involve, for example, manufacture of super insulatingmaterials, lightweight structures, impact dampeners and nonflammablematerials. Three-dimensional porous polyurea networks including polyureaaerogels may be useful in applications that involve, for example,absorption of oil or other hydrophobic materials. In some instances,such materials may be capable of absorbing 5, 15, 20, 25, or more timestheir weight in oil or other hydrophobic material, as illustrativelyshown in FIG. 33. In FIG. 33, a polyurea aerogel is added to containerthat includes Louisiana crude oil on water and after 5 minutes,absorption of the oil is noticeably visible. In some instances, themajority of the substance absorbed may be retrieved by any suitablechemical and/or mechanical method. In some instances, three-dimensionalporous carbon networks including carbon aerogels may also be useful fora number of applications including, for example, manufacture ofelectrodes, batteries, supercapacitors, high-temperature insulators,high temperature ballistics materials, ablative materials, andinfrared-blocking armor.

EXAMPLES

Polyurea aerogels were prepared from monomers of Desmodur N3300Atriisocyanate, Desmodur RE triisocyanate, Desmodur N3200 diisocyanate,toluene diisocyanate (Mondur TDS) and MDI (Mondur CD), obtained fromBayer Corporation. Desmodur RE was supplied as a solution in ethylacetate, which was removed with a rotary evaporator before use.Anhydrous acetone was produced from lower grade solvent by distillingover P₂O₅. Triethylamine (99% pure) was purchased from ACROS and wasdistilled before use.

Polyurea aerogels of different densities were prepared by varying theconcentration of the monomer by dissolving samples of Desmodur N3300A inamounts of 1.375 g, 2.75 g, 5.5 g, 11.0 g, 16.5 g and 33 g in constantvolume (94 mL) of dry acetone. Subsequently, for each monomerconcentration, separate amounts of water at 1.5, 3.0, and 4.5 molequivalents was added, and sols were obtained by adding triethylamine at0.3%, 0.6% and 0.9% w/w relative to the total weight of the isocyanatemonomer plus solvent. The final N3300A monomer concentrations wereapproximately 0.029 M, 0.056 M, 0.11 M, 0.21 M, 0.30 M, and 0.52 M.Thus, in one example, 1.375 g (0.0028 mol) of N3300A was dissolved in 94mL of dry acetone, 1.5 mol equivalents of water (0.073 mL, 0.0042 mol)was added on top and finally the sol was obtained by adding 0.26 mL oftriethylamine (0.3% w/w as defined above). The sol was shaken vigorouslyand was then poured into polypropylene syringes used as molds (AirTiteNorm-Ject syringes without needles purchased from Fisher, Part No.14-817-31, 1.40 mm I.D.). The top part of the syringes were cut off witha razor blade and, after the syringes were filled with the sol, theywere covered with multiple layers of Parafilm and solutions were left togel for approximately 24 h. FIG. 11 depicts a graph of gelation time forthe polyurea aerogels prepared with Desmodur N3300A for water at 1.5,3.0, and 4.5 mol equivalents with triethylamine added at 0.6% w/wrelative to the total weight of the isocyanate monomer plus solvent.Further, FIG. 12 depicts a graph of gelation time for the polyureaaerogels prepared with Desmodur N3300A for triethylamine was added at0.3%, 0.6%, and 0.9% w/w relative to the total weight of the isocyanatemonomer plus solvent with water added at 3.0 mol equivalent. The effectsof the concentration of triethylamine and water on the gelation time areshown in FIG. 13 a. In addition, FIG. 13 b illustrates the effects ofthe concentration of Desmodur N3300A on the gelation time. FIGS. 14 aand 14 b depict further effects that depend on the concentration ofDesmodur N3300A in the sol.

For comparison, gels with other isocyanates (Desmodur RE, Desmodur N3200and Mondur TDS) were made by varying the amount of the monomer in such away that the final molar concentrations of the monomers in the solswould be equal to those used for N3300A. For Desmodur RE triisocyanate,it was possible to obtain gels over the entire concentration range usedwith Desmodur N3300A. Gels from Desmodur N3200 and Mondur TDS wereobtained for monomer concentrations above ˜0.20 M. Formulations andgelation times are summarized in Tables 4-11. Gels were aged for a day.Subsequently, gels were removed from their molds and were placedindividually into fresh acetone ˜4× the volume of each gel. The solventwas exchanged two more times, every 24 h. Finally, wet gels were driedinto polyurea aerogels with CO₂ extracted supercritically.Alternatively, xerogels are obtained by ambient drying of acetone-filledwet gels, while aerogel-like materials are obtained from the two highestdensity samples (those made with [N3300A] at 0.3 or 0.5 M) by exchangingacetone with pentane (4 washes), followed by drying at 40° C. underambient pressure.

Variable density polyurea aerogels were synthesized using a systemsimilar to that shown in FIGS. 9 and 10 by filling a syringe mold asabove using a pump with a high concentration of sol (e.g., [N3300A]=0.52M), which is continuously diluted using a second pump with a lowconcentration sol. The resulting sols became hazy and gelledprogressively from the bottom up. The resulting gels were removed fromthe molds and were processed as the uniform density samples. Thevariable density was confirmed with NMR imaging (MRI) and directmeasurement. Samples were tested for flammability, ignited from thelow-density end, as described further below.

Drying with SCF CO₂ was conducted in an autoclave (SPI-DRY JumboCritical Point Dryer, SPI Supplies, Inc., West Chester, Pa.). Samplessubmerged in the last wash solvent were loaded in the autoclave and wereextracted at 14° C. with liquid CO₂ until no more solvent (acetone) cameout. Then the temperature of the autoclave was raised above the criticalpoint of CO₂ (31.1° C., 73.8 bar), and the pressure was releasedisothermally at 40° C. All dry gels were in cylindrical form so thatbulk (envelope) densities (ρ_(b)) were determined from their mass andvolume, which in turn was determined from the geometric dimensions ofeach sample.

Skeletal densities (ρ_(s)) were determined using helium pycnometry witha Micromeritics AcuuPyc II 1340 instrument. Porosities, Π, weredetermined from the ρ_(b) and ρ_(s) values according to:P=100×[(1/ρ_(b))−(1/ρ_(s))]/(1/ρ_(b)). Surface areas (σ) were measuredby nitrogen sorption porosimetry using a Micromeritics ASAP 2020 SurfaceArea and Pore Distribution Analyzer. Samples for surface area andskeletal density determinations were outgassed for 24 h at 80° C. undervacuum before analysis. Polyurea aerogels were characterized chemicallyby infrared spectroscopy (IR) in KBr compressed pellets using aNicolet-FTIR Model 750 Spectrometer, and by solids ¹³C NMR spectroscopywith samples ground in fine powders on a Bruker Avance 300 Spectrometerwith 75.475 MHz carbon frequency using magic angle spinning (at 7 kHz),7 mm rotors, broad band proton suppression, and the CPMAS TOSS pulsesequence for spin sideband suppression. The operating frequency for ¹³Cwas 75.483 MHz. ¹³C NMR spectra were externally referenced to thecarbonyl of glycine (176.03 ppm relative to tetramethylsilane). SEM wasconducted with samples coated with Au—Pd using a Hitachi S-4700 fieldemission microscope. The crystallinity of the polyurea samples wasdetermined by x-ray diffraction (XRD) using a Scintag 2000diffractometer with Cu Kα radiation and a proportional counter detectorequipped with a flat graphite monochromator. The identity of thefundamental building blocks of the two materials was probed with smallangle neutron scattering (SANS) using ˜2 mm thick discs cut with adiamond saw from cylinders, on a time of flight, low-Q diffractometer,LQD, at the Manuel Lujan Jr. Scattering Center of the Los AlamosNational Laboratory. The scattering data were reported in the absoluteunits of differential cross section per unit volume (cm⁻¹) as a functionof Q, the momentum transferred during a scattering event.Thermogravimetric analysis TGA was conducted under N₂, with a TAInstruments Model 2920 apparatus at a heating rate of 10° C./min.Quasistatic mechanical characterization (compression testing) wasconducted according to the ASTM D695-02a standard on cylindricalspecimens, using a MTS machine (Model 810) equipped with a 55000 lb loadcell, as described previously. According to that ASTM standard, theheight-to-diameter ratio of the specimen should be 2:1; typical sampleswere ˜1.3 cm in diameter, ˜2.6 cm long.

FIGS. 15 a and 15 b show NMR spectra and IR spectra confirming thereaction of isocyanate and formation of polyurea aerogels. IR spectra ofDesmodur N3300A versus PUA aerogels illustrate complete reaction of theisocyanate by the disappearance of the isocyanate stretch at ˜2500 cm⁻¹,and formation of the —NH and carbonyl stretches at ˜3300 cm⁻¹ and ˜1700cm⁻¹ (shoulder), respectively. ¹³C NMR spectra of N3300A versus PUAaerogels confirm formation of PUA by the disappearance of the N═C═Oresonance at 121 ppm, and the appearance of the urea C=0 resonance at159 ppm.

FIG. 16 depicts an XRD analysis of polyurea aerogels showing increasingcrystallinity as a function of increasing density, also illustrating themolarity of monomer as well. FIG. 17 shows an XRD analysis of polyureaaerogels prepared with different monomers and the respective degree ofcrystallinity. By XRD, the degree of crystallinity of PUA aerogelsprepared from Desmodur N3300A is 35%, but PUA aerogels prepared fromDesmodur N3200 and TMT showed almost no crystallinity. This is mostprobably related to the particulate nanomorphology of those samples.

A number of SEM images will now be described. The SEM image of FIG. 18 ashows a low density polyurea aerogel having a density of 0.15 g/cm³ anda porosity of 98%. FIG. 18 b shows a SEM image of a high densitypolyurea aerogel having a density of 0.54 g/cm³ and a porosity of 54%.FIG. 19 depicts SEM images of polyurea aerogels under a constantconcentration of N3300A at different gelation times illustrating thatthe nano-morphology of polyurea aerogels described herein might notdepend on the concentration of catalyst and water. FIG. 20 shows SEMimages and graphs that show that nano-morphology may depend on theconcentration of monomer. FIG. 21 shows SEM images that demonstrate thatwhile incorporating lower concentrations of monomer may yield fibrouspolyurea aerogels, incorporating higher concentrations of monomer mayyield more particulate polyurea aerogels. FIG. 22 illustrates SEM imagesof polyurea aerogels prepared with the more rigid TMT, including bothfibrous and particulate type morphologies. FIG. 23 depicts SEM images ofpolyurea aerogels prepared with diisocyanate monomer, in this example,giving rise to a more particulate nano-morphology. For a polyureaaerogel exhibiting a density gradient (between 2.75 g and 33 g ofmonomer incorporated), FIG. 24 shows SEM images of a high densityportion of a polyurea aerogel and FIG. 25 depicts SEM images of a lowdensity portion of a polyurea aerogel.

The behavior under compression of high density PUA aerogels wasassessed, with results shown in FIGS. 26 and 27. At room temperature,the ultimate strength for the high density PUA aerogels (density=0.55 gcm⁻³) was determined to be 640 MPa. The specific energy absorptiondensity of PUA aerogels calculated from the area under the stress-straincurve was 105,000 Nm/kg. FIG. 27 depicts a compressive stress-straincurve for a high density polyurea aerogel (density of 0.54 g/cm³)prepared from Desmodur N3300A.

In the example illustrated in FIG. 29 a, the polyurea aerogel wasobtained from N3300A and N3200 melt at less than or equal to 200 C andconverted to a carbon aerogel. For the example of FIG. 29 b, thepolyurea aerogel was obtained from TMT to yield carbon aerogels uponpyrolysis under Ar at 800 C. FIG. 30 a shows XRD data of carbon obtainedfrom a polyurea aerogel prepared from TMT. FIG. 30 b shows raman spectraof carbon obtained from a polyurea aerogel prepared from TMT. Carbonobtained from TMT polyurea aerogels were generally nanocrystalline.

The synthesis of homogeneous samples and density gradient samples ofpolyurea aerogels, their materials characterization, and certainapplication specific properties are described.

Synthesis of uniform-density polyurea (PUA) aerogels and a photograph orrepresentative samples made of Desmodur N3300A (densities reported belowfor each sample are in mg cm⁻³) is shown in FIG. 8. Gelation is inducedby adding water and Et₃N in a solution of a polyfunctional isocyanate inacetone. Sols become progressively hazy and eventually turn into whitegels. All samples able to gel can also be dried by extraction withliquid CO₂ taken out at the end as a SCF, yielding robust aerogelmonoliths (see above photograph). Gelation of triisocyanates (aliphaticDesmodur N3300A and aromatic Desmodur RE) takes place with monomerconcentrations as low as 0.029 M, while gelation of diisocyanates(aliphatic Desmodur N3200, and aromatic toluene diisocyanates (MondurTDS) and 4,4′-methylene diphenyl diisocyanates (Mondur CD)) takes placeonly at higher monomer concentrations (>0.2 M, see Tables 4-11). UsingDesmodur N3300A triisocyanate as a model system, the gelation time(Tables 4-9) decreases with increasing concentrations of the isocyanate,while the concentration effect of water and the catalyst (Et₃N) is morepronounced at lower monomer concentrations. Taking the gelation time asa rate indicator for the gelation process, it is found that within errorthis is first order in both H₂O and Et₃N. Sols without Et₃N gel in muchlonger time periods (days), while use of OH⁻ as catalyst (introduced asNH₄OH) accelerates the process causing fast precipitation rather thangelation. Gelation proceeds qualitatively similarly in acetonitrile,while in DMSO it takes place very fast causing large bubbles of CO₂ tobe trapped in translucent gels. DMSO-derived gels combine largefoam-like macroporosity with nanoporous walls similar to those obtainedin acetone or acetonitrile as described further below.

Wet gels were aged to ensure complete reaction of the monomer,solvent-exchanged (washed) with pure acetone and dried in an autoclavewith liquid CO₂ taken out at the end as a SCF. Washes were collected andno residual (unreacted) isocyanate was detected. Acetone wet gels areleft to dry under ambient conditions and undergo extensive shrinkage andyield xerogel-like materials. Alternatively, by applying a methoddeveloped with polyurea-crosslinked silica aerogels, wet gels made withthe two highest isocyanate concentrations (˜0.3 and 0.5 M) andsolvent-exchanged with a low vapor pressure/surface tension solvent likepentane can be dried under ambient pressure at slightly elevatedtemperature (e.g., 40° C.), yielding materials similar in appearance andproperties to those obtained by the SCF CO₂ route. Ambient pressuredrying was used for making larger monolithic aerogel pieces forevaluation in certain aeronautical and anti-ballistic applications.

Density-gradient polyurea aerogel samples were prepared using two pumps,one to transfer high concentration sol into a mold, while a second pumptransfers and constantly dilutes the high concentration sol with a lowconcentration one the low concentration sol could be replaced withsolvent. To minimize convective mixing of the two solutions in the mold,a rubber O-ring was fit inside the upper lip of the cylindrical mold,connected to a vertical wire. The sol slides down the wire, is spreadaround by the ring and slides down again along the inside walls of themold. Appearance-wise, density-gradient aerogels were monolithic andindistinguishable from the uniform-density samples.

Tables 1-3: Various Gelation Times for Samples Prepared Above

TABLE 1 Time for gelation of low-density polyurea aerogels with varyingconcentrations of water and triethylamine. Weight of Equiv- Sampletriisocyanate alent of % TEA No. monomer (g) Water (w/w) Gelation time 15.5 1.5× 0.3 8.5 hours 2 5.5 1.5× 0.6 3 5.5 1.5× 0.9 4 5.5 3.0× 0.3 6hours 5 5.5 3.0× 0.6 3 hours 6 5.5 3.0× 0.9 1 hour 7 5.5 4.5× 0.3 5.5hours 8 5.5 4.5× 0.6 9 5.5 4.5× 0.9 33 minutes

TABLE 2 Time for gelation of medium-density polyurea aerogels withvarying concentrations of water and triethylamine. Weight of Equiv-Sample triisocyanate alent of % TEA No. monomer (g) Water (w/w) Gelationtime 1 11.0 1.5× 0.3  4 hours 2 11.0 1.5× 0.6 3 11.0 1.5× 0.9 4 11.03.0× 0.3  3 hours 5 11.0 3.0× 0.6  1 hour 20 minutes 6 11.0 3.0× 0.9  1hour 7 11.0 4.5× 0.3  1 hour 30 minutes 8 11.0 4.5× 0.6 9 11.0 4.5× 0.933 minutes

TABLE 3 Time for gelation of high-density polyurea aerogels with varyingconcentrations of water and triethylamine. Weight of triisocyanateEquivalent of Sample No. monomer (g) Water % TEA (w/w) Gelation time 116.5 1.5× 0.3 2 hours 2 16.5 1.5× 0.6 3 16.5 1.5× 0.9 4 16.5 3.0× 0.3 1hour 5 16.5 3.0× 0.6 34 minutes 6 16.5 3.0× 0.9 24 minutes 7 16.5 4.5×0.3 38 minutes 8 16.5 4.5× 0.6 9 16.5 4.5× 0.9 15 minutes

Formulations and Gelation Times of Samples Using Desmodur N3300A,Desmodur N3200, Desmodur RE and Mondur TDS

TABLE 4 Gelation times of Desmodur N3300A sols, at the 1.375 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³ amount ofmol equivalents % w/w concentration N3300A in sol of H₂O Et₃N of (g)(mL) (mL) N3300 A (M) gelation time 1.375 1.5 (0.073) 0.3 (0.26) 0.0286~24 h 1.375 1.5 (0.073) 0.6 (0.52) 0.0285 ~20 h 1.375 1.5 (0.073) 0.9(0.78) 0.0284 ~19 h 1.375 3.0 (0.147) 0.3 (0.26) 0.0285 ~17 h 1.375 3.0(0.147) 0.6 (0.52) 0.0285 ~15 h 30 min 1.375 3.0 (0.147) 0.9 (0.78)0.0284 ~12 h 1.375 4.5 (0.219) 0.3 (0.26) 0.0285 ~10 h 1.375 4.5 (0.219)0.6 (0.52) 0.0284  ~9 h 30 min 1.375 4.5 (0.219) 0.9 (0.78) 0.0284  ~9 h

TABLE 5 Gelation times of Desmodur N3300A sols, at the 2.75 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³ amount ofmol equiv- % w/w concentration N3300A in sol alents of Et₃N of gelation(g) H₂O (mL) (mL) N3300A (M) time 2.75 1.5 (0.147) 0.3 (0.266) 0.0564~18 h 2.75 1.5 (0.147) 0.6 (0.532) 0.0562 ~17 h 2.75 1.5 (0.147) 0.9(0.798) 0.0561 ~14 h 2.75 3.0 (0.295) 0.3 (0.266) 0.0563 ~12 h 2.75 3.0(0.295) 0.6 (0.532) 0.0561  ~9 h 2.75 3.0 (0.295) 0.9 (0.798) 0.0560  ~8h 30 min 2.75 4.5 (0.441) 0.3 (0.266) 0.0562  ~6 h 2.75 4.5 (0.441) 0.6(0.532) 0.0561  ~4 h 30 min 2.75 4.5 (0.441) 0.9 (0.798) 0.0559  ~3 h

TABLE 6 Gelation times of Desmodur N3300A sols, at the 5.5 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³ amount ofN3300A mol equiv- % w/w concen- in sol alents of Et₃N tration of (g) H₂O(mL) (mL) N3300A (M) gelation time 5.5 1.5 (0.295) 0.3 (0.327) 0.1099 8h 35 min 5.5 1.5 (0.295) 0.6 (0.654) 0.1095 ~8 h 5.5 1.5 (0.295) 0.9(0.981) 0.1092 7 h 40 min 5.5 3.0 (0.589) 0.3 (0.327) 0.1095 6 h 5.5 3.0(0.589) 0.6 (0.654) 0.1092 3 h 5.5 3.0 (0.589) 0.9 (0.981) 0.1088 1 h11.0 1.5 (0.589) 0.3 (0.35) 0.2092 4 h 11.0 1.5 (0.589) 0.6 (0.70)0.2085 3 h 33 min 11.0 1.5 (0.589) 0.9 (1.05) 0.2078 ~3 h 11.0 3.0(1.178) 0.3 (0.35) 0.2080 ~3 h 11.0 3.0 (1.178) 0.6 (0.70) 0.2073 l h 20min 11.0 3.0 (1.178) 0.9 (1.05) 0.2066 1 h 11.0 4.5 (1.767) 0.3 (0.35)0.2068 1 h 30 min 11.0 4.5 (1.767) 0.6 (0.70) 0.2062 ~45 min 11.0 4.5(1.767) 0.9 (1.05) 0.2055 30 min 5.5 4.5 (0.884) 0.3 (0.327) 0.1092 5 h30 min 5.5 4.5 (0.884) 0.6 (0.654) 0.1088 ~2 h 5.5 4.5 (0.884) 0.9(0.981) 0.1085 1 h 33 min

TABLE 7 Gelation times of Desmodur N3300A sols, at the 11 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³

indicates data missing or illegible when filed

TABLE 8 Gelation times of Desmodur N3300A sols, at the 16.5 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³ amount ofmol equiv- % w/w concentra- N3300A in sol alents of Et₃N tion ofgelation (g) H₂O (mL) (mL) N3300A (M) time 16.5 1.5 (0.884) 0.3 (0.375)0.2994 2 h  16.5 1.5 (0.884) 0.6 (0.75) 0.2983 1 h 20 min 16.5 1.5(0.884) 0.9 (1.125) 0.2973 1 h 10 min 16.5 3.0 (1.767) 0.3 (0.375)0.2970 1 h  16.5 3.0 (1.767) 0.6 (0.75) 0.2960 34 min 16.5 3.0 (1.767)0.9 (1.125) 0.2950 24 min 16.5 4.5 (2.650) 0.3 (0.375) 0.2946 38 min16.5 4.5 (2.650) 0.6 (0.75) 0.2936 25 min 16.5 4.5 (2.650) 0.9 (1.125)0.2926 15 min

TABLE 9 Gelation times of Desmodur N3300A sols, at the 33 g in 94 mLacetone formulation, as a function of the amount of water andtriethylamine (Et₃N) Density of Desmodur N3300A: 1.17 g cm⁻³ amount ofmol equiv- % w/w concentra- N3300A in sol alents of Et₃N tion ofgelation (g) H₂O (mL) (mL) N3300A (M) time 33.0 1.5 (1.767) 0.3 (0.439)0.5263 ~1 h 33.0 1.5 (1.767) 0.6 (0.878) 0.5244 ~45 min 33.0 1.5 (1.767)0.9 (1.32) 0.5226 ~35 min 33.0 3.0 (3.53) 0.3 (0.439) 0.5189 ~35 min33.0 3.0 (3.53) 0.6 (0.878) 0.5171 ~20 min 33.0 3.0 (3.53) 0.9 (1.32)0.5153 10 min 33.0 4.5 (5.30) 0.3 (0.439) 0.5118 10 min 33.0 4.5 (5.30)0.6 (0.878) 0.5100 5 min 33.0 4.5 (5.30) 0.9 (1.32) 0.5082 5 min

TABLE 10 Gelation times of Desmodur N3200 sols, at the middle water andtriethylamine (Et₃N) formulations (refer to Desmodur N3300A, Tables4-9); Solvent: acetone, 94 mL Density of Desmodur N3200: 1.13 g cm⁻³amount of mol equiv- N3200 in sol alents of % w/w Et₃N concentration (g)H₂O (mL) (mL) of N3200 (M) gelation time 1.3 3.0 (0.147) 0.6 (0.618)0.0283 no gelation 2.6 3.0 (0.294) 0.6 (0.628) 0.0560 no gelation 5.23.0 (0.588) 0.6 (0.650) 0.1091 no gelation 10.4 3.0 (1.177) 0.6 (0.696)0.2066 30 min 15.6 3.0 (1.765) 0.6 (0.735) 0.2955 15 min 31.2 3.0 (3.53)0.6 (0.864) 0.5166  5 min

TABLE 11 Gelation times of 4,4′,4″-triphenylmethane triisocyanate sols(TMT, from Desmodur RE), at the middle water and triethylamine (Et₃N)formulations (refer to Desmodur N3300A, Tables 4-9); Solvent: acetone,94 mL Density of TMT: 1.015 g cm⁻³ amount of mol equiv- TMT in solalents of % w/w Et₃N concentration of (g) H₂O (mL) (mL) TMT (M) gelationtime 1 3.0 (0.147) 0.6 (0.61) 0.0284 ~36 h 2 3.0 (0.294) 0.6 (0.62)0.0563 24 h 4 3.0 (0.588) 0.6 (0.64) 0.1099 ~9 h 8 3.0 (1.177) 0.6(0.674) 0.2101 2 h 12 3.0 (1.765) 0.6 (0.706) 0.3019 45 min 24 3.0(3.53) 0.6 (0.80) 0.5360 10 min

TABLE 12 Gelation times of Mondur TDS (toluene isocyanate, TDI) sols, atthe middle water and triethylamine (Et₃N) formulations (refer toDesmodur N3300A, Tables 4-9); Solvent: acetone, 94 mL Density of MondurTDS: 1.214 g cm⁻³ amount of mol equiv- % w/w concentra- Mondur TDS insol alents of Et₃N tion of gelation (g) H₂O (mL) (mL) TDI (M) time 0.4743.0 (0.147) 0.6 (0.61) 0.0286 no gelation 0.947 3.0 (0.294) 0.6 (0.614)0.0568 no gelation 1.89 3.0 (0.588) 0.6 (0.622) 0.1121 no gelation 3.793.0 (1.177) 0.6 (0.64) 0.2201 5 min 5.68 3.0 (1.765) 0.6 (0.67) 0.3213 2min 11.36 3.0 (3.53) 0.6 (0.72) 0.5886 <1 min  Comparison of PUA Xerogel, Aerogels and Samples Dried from Pentane

TABLE 13 The effect of the drying conditions on selected properties ofpolyurea (PUA) aerogels prepared with Desmodur N3300A triisocyanateusing the middle water and triethylamine (Et₃N) formulations, that is3.0 mol equivalents of water and 0.6% w/w triethylamine (refer to Tables4-9) bulk skeletal porosity, Π concentration diameter shrinkage density,density, (% v/v of N3300A (M) (cm) (%) ^(e) ρ_(b) (g cm⁻³) ρ_(s) (gcm⁻³) ^(f) void space) 0.0285 xerogel ^(a,b) 0.38 73.0 0.932 1.21 ± 0.1522.3 aerogel ^(c) 1.28 ± 0.01 13.3 ± 0.6 0.016 ± 0.000₄ 1.24 ± 0.23 98.6pentane-died ^(d,b) 0.42 70.0 0.734 1.23 ± 0.31 40.3 0.0561 xerogel^(a,b) 0.44 68.5 0.951 1.25 ± 0.18 23.9 aerogel ^(c) 1.35 ± 0.01  9.1 ±0.9 0.034 ± 0.000₄ 1.31 ± 0.06 97.5 pentane-died ^(d,b) 0.48 65.7 0.6671.27 ± 0.28 47.5 0.1092 xerogel ^(a,b) 0.56 60.0 0.988 1.21 ± 0.22 18.3aerogel ^(c) 1.27 ± 0.01 14.8 ± 0.2 0.072 ± 0.005 1.21 ± 0.03 93.9pentane-died ^(d,b) 0.57 59.2 0.719 1.264 ± 0.24  43.0 0.2073 xerogel^(a,b) 0.66 52.8 1.01 1.22 ± 0.26 17.2 aerogel ^(c) 1.32 ± 0.01 10.6 ±0.2 0.126 ± 0.001 1.30 ± 0.07 90.3 pentane-died ^(d,b) 0.74 47.1 0.6401.21 ± 0.25 47.1 0.2960 xerogel ^(a,b) 0.76 45.7 1.03  1.28 ± 0.14 19.5aerogel ^(c) 1.27 ± 0.03 14.1 ± 1.8 0.192 ± 0.012 1.21 ± 0.02 84.2pentane-died ^(d,b) 1.20 14.2 0.243 1.23 ± 0.15 80.2 0.5171 xerogel^(a,b) 0.92 34.2 1.04 1.29 ± 0.28 19.3 aerogel ^(c) 1.11 ± 0.02   25 ±1.4  0.55 ± 0.03  1.2 ± 0.001 54.1 pentane-died ^(d,b) 1.14 18.5 0.4901.19 ± 0.13 58.8 ^(a) Acetone-soaked wet-gels dried under ambienttemperature and pressure. ^(b) Single sample. ^(c) Average of 5 samplesdried with SCF CO₂. ^(d) Pentane-soaked wet-gels dried under ambientpressure at 40° C. ^(e) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). Mold diameter: 1.40 cm. ^(f) Single sample,average of 50 measurements.

TABLE 14 Selected properties of PUA aerogels prepared using about0.0285M of Desmodur N3300A triisocyanate (refer to Table 4)and all waterand triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5 molequivalents of water and 0.3, 0.6, and 0.9% w/w triethylamine H₂O—Et₃Nbulk skeletal porosity, BET surface average particle (×mol- diametershrinkage density, density, II (% void area, σ pore diameter radius, %w/w) (cm) ^(a) (%) ^(a,) ^(b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³) ^(c)space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3  1.3 ± 0.016 12.5 ± 1.30.016 ± 0.001 1.28 ± 0.12 98.7 159.8 8.5 [1545] 14.6 1.5-0.6 1.27 ±0.005 14.0 ± 0.3 0.015 ± 0.002 1.32 ± 0.01 98.8 230.1 13.5 [1145] 9.91.5-0.9 1.27 ± 0.012 14.3 ± 0.9 0.017 ± 0.001 1.29 ± 0.03 98.6 162.2 8.9[1433] 14.3 3.0-0.3 1.28 ± 0.008 13.3 ± 0.56 0.017 ± 0.0006 1.25 ± 0.1898.6 288.9 11.7 [803] 8.3 3.0-0.6 1.28 ± 0.008 13.3 ± 0.56 0.016 ±0.0004 1.24 ± 0.23 98.6 222.4 12.0 [1109] 10.8 3.0-0.9 1.29 ± 0.009 13.0± 0.61 0.017 ± 0.001 1.25 ± 0.22 98.7 131.2 10.5 [1769] 18.2 4.5-0.31.29 ± 0.009 12.8 ± 0.47 0.016 ± 0.0006 1.24 ± 0.28 98.6 157.5 11.0[1566] 15.3 4.5-0.6 1.30 ± 0.011 12.5 ± 0.75 0.016 ± 0.0009 1.24 ± 0.2598.8 150.9 11.5 [1635] 16.0 4.5-0.9 1.29 ± 0.005 13.1 ± 0.33 0.016 ±0.001 1.28 ± 0.31 98.7 199.5 10.5 [1237] 11.7 ^(a) Average of 5 samples.(Mold diameter: 1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). ^(c) Single sample, average of 50measurements. ^(d) By the 4 × V_(Total)/σmethod. For the first number,V_(Total) was calculated by the single-point adsorption method; for thenumber in brackets V_(Total) was calculated via V_(Total) = (1/ρ_(b)) −(1/ρ_(s)). ^(e) Calculated via r = 3/ρ_(s)σ.

TABLE 15 Selected properties of PUA aerogels prepared using about0.0561M of Desmodur N3300A triisocyanate (refer to Table 5) and allwater and triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5mol equivalents of water and 0.3, 0.6, and 0.9% w/w triethylamineH₂O—Et₃N bulk skeletal porosity, BET surface average particle (×mol-diameter shrinkage density, density, II (% void area, σ pore diameterradius, % w/w) (cm) ^(a) (%) ^(a, b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³)^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3 1.32 ± 0.008 11.1 ±0.54 0.031 ± 0.002 1.25 ± 0.04 97.5 216.2 16.8 [581] 11.1 1.5-0.6 1.31 ±0.009 11.5 ± 0.6 0.032 ± 0.003 1.25 ± 0.03 97.6 231.6 13.5 [526] 10.41.5-0.9 1.30 ± 0.019 12.2 ± 0.74 0.033 ± 0.002 1.25 ± 0.04 97.6 271.718.1 [434] 8.8 3.0-0.3 1.32 ± 0.007 10.7 ± 0.50 0.034 ± 0.002 1.27 ±0.04 97.6 230.3 19.1 [497] 10.3 3.0-0.6 1.35 ± 0.012 9.12 ± 0.85 0.034 ±0.0004 1.31 ± 0.06 97.5 243.5 20.4 [471] 9.4 3.0-0.9 1.32 ± 0.005 11.1 ±0.33 0.033 ± 0.0008 1.27 ± 0.05 97.4 281.3 10.5 [420] 8.4 4.5-0.3 1.33 ±0.01 10.4 ± 0.69 0.032 ± 0.011 1.27 ± 0.06 97.5 304.2 11.0 [401] 7.84.5-0.6 1.32 ± 0.01 10.7 ± 0.66 0.033 ± 0.001 1.28 ± 0.06 97.3 255.516.3 [462] 9.2 4.5-0.9 1.32 ± 0.005 10.5 ± 0.33 0.032 ± 0.001 1.28 ±0.05 97.3 236.7 14.0 [514] 9.9 ^(a) Average of 5 samples. (Molddiameter: 1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). ^(c) Single sample, average of 50measurements. ^(d) By the 4 × V_(Total)/σmethod. For the first number,V_(Total) was calculated by the single-point adsorption method; for thenumber in brackets V_(Total) was calculated via V_(Total) = (1/ρ_(b)) −(1/ρ_(s)). ^(e) Calculated via r = 3/ρ_(s)σ.

TABLE 16 Selected properties of PUA aerogels prepared using about0.1092M of Desmodur N3300A triisocyanate (refer to Table 6) and allwater and triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5mol equivalents of water and 0.3, 0.6, and 0.9% w/w triethylamineH₂O—Et₃N bulk skeletal porosity, BET surface average particle (×mol-diameter shrinkage density, density, II (% void area, σ pore diameterradius, % w/w) (cm) ^(a) (%) ^(a, b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³)^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3 1.28 ± 0.009 13.5 ±0.41 0.072 ± 0.008 1.24 ± 0.16 94.1 177.6 23.3 [292.6] 13.6 1.5-0.6 1.32± 0.004 10.6 ± 0.32 0.069 ± 0.001 1.24 ± 0.01 94.4 198.8 27.7 [275.3]12.1 1.5-0.9 1.28 ± 0.021 13.6 ± 1.42 0.077 ± 0.003 1.26 ± 0.02 93.6200.2 25.9 [239.7] 11.8 3.0-0.3 1.31 ± 0.06 11.4 ± 0.32 0.070 ± 0.0031.24 ± 0.12 94.4 182.8 25.7 [293] 13.2 3.0-0.6 1.27 ± 0.01 14.8 ± 0.180.072 ± 0.005 1.21 ± 0.03 93.9 234.7 23.6 [222.5] 10.5 3.0-0.9 1.25 ±0.03 16.6 ± 0.42 0.073 ± 0.005 1.20 ± 0.01 93.8 185.0 28.8 [276] 13.54.5-0.3  1.3 ± 0.02 12.3 ± 0.50 0.069 ± 0.001 1.22 ± 0.01 94.5 176.432.5 [310] 13.9 4.5-0.6 1.31 ± 0.01 11.4 ± 0.78 0.064 ± 0.002 1.26 ±0.02 95.1 174.7 32.5 [339] 13.6 4.5-0.9 1.27 ± 0.02 14.1 ± 1.21 0.070 ±0.002 1.22 ± 0.03 94.1 167.9 19.7 [318] 14.6 ^(a) Average of 5 samples.(Mold diameter: 1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). ^(c) Single sample, average of 50measurements. ^(d) By the 4 × V_(Total)/σmethod. For the first number,V_(Total) was calculated by the single-point adsorption method; for thenumber in brackets V_(Total) was calculated via V_(Total) = (1/ρ_(b)) −(1/ρ_(s)). ^(e) Calculated via r = 3/ρ_(s)σ.

TABLE 17 Selected properties of PUA aerogels prepared using about0.2073M of Desmodur N3300A triisocyanate (refer to Table 7) and allwater and triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5mol equivalents of water and 0.3, 0.6, and 0.9% w/w triethylamineH₂O—Et₃N bulk skeletal porosity, BET surface average particle (×mol-diameter shrinkage density, density, II (% void area, σ pore diameterradius, % w/w) (cm) ^(a) (%) ^(a, b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³)^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3 1.30 ± 0.011 12.1 ±0.79 0.131 ± 0.005 1.26 ± 0.03 89.6 177.4 19.5 [154] 13.4 1.5-0.6 1.33 ±0.02 10.3 ± 1.4 0.128 ± 0.004 1.23 ± 0.02 89.6 171.9 34.1 [163] 14.11.5-0.9 1.30 ± 0.007 12.1 ± 0.42 0.128 ± 0.0007 1.24 ± 0.03 89.7 154.636.1 [181] 15.6 3.0-0.3 1.32 ± 0.01 10.6 ± 1.01 0.126 ± 0.004 1.22 ±0.01 89.7 200.1 32.1 [142.1] 12.2 3.0-0.6 1.32 ± 0.01 10.6 ± 0.18 0.126± 0.001 1.30 ± 0.07 90.3 169.4 33.4 [169.3] 13.6 3.0-0.9 1.33 ± 0.0110.3 ± 0.55 0.127 ± 0.003 1.20 ± 0.01 89.3 153.4 26.3 [183.5] 16.24.5-0.3 1.32 ± 0.01 10.6 ± 0.67 0.125 ± 0.005 1.24 ± 0.02 89.9 123.720.4 [233] 19.5 4.5-0.6 1.33 ± 0.01 10.4 ± 0.37 0.122 ± 0.001 1.25 ±0.02 90.2 133.6 23.5 [241] 17.9 4.5-0.9 1.32 ± 0.02 10.6 ± 0.28 0.130 ±0.006 1.25 ± 0.03 90.7 126.0 18.1 [218] 19.0 ^(a) Average of 5 samples.(Mold diameter: 1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). ^(c) Single sample, average of 50measurements. ^(d) By the 4 × V_(Total)/σmethod. For the first number,V_(Total) was calculated by the single-point adsorption method; for thenumber in brackets V_(Total) was calculated via V_(Total) = (1/ρ_(b)) −(1/ρ_(s)). ^(e) Calculated via r = 3/ρ_(s)σ.

TABLE 18 Selected properties of PUA aerogels prepared using about0.2960M of Desmodur N3300A triisocyanate (refer to Table 8) and allwater and triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5mol equivalents of water and 0.3, 0.6, and 0.9% w/w triethylamineH₂O—Et₃N bulk skeletal porosity, BET surface average particle (×mol-diameter shrinkage density, density, II (% void area, σ pore diameterradius, % w/w) (cm) ^(a) (%) ^(a, b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³)^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3 1.28 ± 0.03 13.3 ±2.09 0.194 ± 0.01 1.19 ± 0.01 83.8 51.67 21.5 [333] 48.7 1.5-0.6 1.28 ±0.01 13.4 ± 0.88 0.212 ± 0.004 1.25 ± 0.01 83.1 153.5 23.6 [102] 15.61.5-0.9 1.29 ± 0.02 12.7 ± 1.11 0.194 ± 0.0007 1.23 ± 0.01 84.2 153.129.1 [113] 15.9 3.0-0.3 1.31 ± 0.01 11.1 ± 0.85 0.181 ± 0.003 1.18 ±0.01 84.7 149.1   19.7 [125.4] 17.1 3.0-0.6 1.27 ± 0.03 14.1 ± 1.780.192 ± 0.012 1.21 ± 0.02 84.2 67.5 27.8 [259] 36.7 3.0-0.9 1.27 ± 0.0213.9 ± 1.48 0.197 ± 0.009 1.22 ± 0.01 83.8 49.2 13.4 [345] 49.9 4.5-0.31.28 ± 0.04 13.5 ± 2.4 0.189 ± 0.008 1.21 ± 0.01 84.4 68.9 23.6 [259]35.9 4.5-0.6 1.26 ± 0.01 15.1 ± 0.77  0.22 ± 0.01 1.23 ± 0.01 82.2 51.023.3 [292] 47.8 4.5-0.9 1.27 ± 0.02 14.4 ± 1.45 0.191 ± 0.01 1.23 ± 0.0284.5 24.8 23.1 [712] 98.3 ^(a) Average of 5 samples. (Mold diameter:1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − mold diameter)/(molddiameter). ^(c) Single sample, average of 50 measurements. ^(d) By the 4× V_(Total)/σmethod. For the first number, V_(Total) was calculated bythe single-point adsorption method; for the number in brackets V_(Total)was calculated via V_(Total) = (1/ρ_(b)) − (1/ρ_(s)). ^(e) Calculatedvia r = 3/ρ_(s)σ.

TABLE 19 Selected properties of PUA aerogels prepared using about0.5171M of Desmodur N3300A triisocyanate (refer to Table 9) and allwater and triethylamine (Et₃N) formulations, that is 1.5, 3.0, and 4.5mol equivalents of water and 0.3, 0.6, and 0.9% w/w triethylamineH₂O—Et₃N bulk skeletal porosity, BET surface average particle (×mol-diameter shrinkage density, density, II (% void area, σ pore diameterradius, % w/w) (cm) ^(a) (%) ^(a, b) ρ_(b) (g cm⁻³) ^(a) ρ_(s) (g cm⁻³)^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e) 1.5-0.3 1.13 ± 0.03 23.5 ±1.37 0.56 ± 0.02 1.19 ± 0.001 53.2 53.3 31.1 [70.5] 47.2 1.5-0.6 1.12 ±0.01 24.2 ± 0.88 0.56 ± 0.02 1.19 ± 0.001 53.2 52.7 22.7 [71.3] 47.81.5-0.9 1.12 ± 0.02 24.5 ± 1.11 0.54 ± 0.04 1.20 ± 0.001 84.2 46.9 33.3[86.7] 53.3 3.0-0.3 1.12 ± 0.01 24.6 ± 0.85 0.54 ± 0.02 1.19 ± 0.00254.5 56.9 26.7 [70.9] 44.3 3.0-0.6 1.11 ± 0.02   25 ± 1.35 0.55 ± 0.03 1.2 ± 0.001 54.1 53.8 31.9 [73.3] 46.4 3.0-0.9  1.1 ± 0.02 25.5 ± 1.30.55 ± 0.03  1.2 ± 0.002 54 52.7 14.8 [74.8] 47.4 4.5-0.3  1.1 ± 0.0225.5 ± 1.3 0.54 ± 0.04  1.2 ± 0.01 54.9 57 26.7 [71.3] 45.5 4.5-0.6 1.08± 0.04 26.5 ± 0.3 0.56 ± 0.02  1.2 ± 0.02 52.5 71.7 25.1 [52.8] 34.84.5-0.9  1.1 ± 0.02 25.8 ± 0.7 0.54 ± 0.02  1.2 ± 0.01 55.2 56.1 29.6[72.8] 45.2 ^(a) Average of 5 samples. (Mold diameter: 1.40 cm.) ^(b)Shrinkage = 100 × (sample diameter − mold diameter)/(mold diameter).^(c) Single sample, average of 50 measurements. ^(d) By the 4 ×V_(Total)/σmethod. For the first number, V_(Total) was calculated by thesingle-point adsorption method; for the number in brackets V_(Total) wascalculated via V_(Total) = (1/ρ_(b)) − (1/ρ_(s)). ^(e) Calculated via r= 3/ρ_(s)σ.

TABLE 20 Selected properties of PUA aerogels prepared with DesmodurN3200 diisocyanate using the middle water and triethylamine (Et₃N)formulations, that is 3.0 mol equivalents of water and 0.6% w/wtriethylamine (refer to Table 10) [N3200] bulk skeletal porosity, BETsurface average particle in sol diameter shrinkage density, density, II(% void area, σ pore diameter radius, (M) (cm) ^(a) (%) ^(a, b) ρ_(b) (gcm⁻³) ^(a) ρ_(s) (g cm⁻³) ^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e)0.2066 1.26 ± 0.01 14.6 ± 1.0 0.175 ± 0.007 1.15 ± 0.01 84.6 4.3 7.4[8.2] 606 0.2955 1.13 ± 0.01 24.7 ± 0.8  0.37 ± 0.01 1.15 ± 0.01 68.512.8 8.5 [9.1] 203 0.5166 1.05 ± 0.05 14.3 ± 0.9  0.54 ± 0.07 1.15 ±0.03 52.7 23.6 12.05 [12.3]  110 ^(a) Average of 5 samples. (Molddiameter: 1.40 cm.) ^(b) Shrinkage = 100 × (sample diameter − molddiameter)/(mold diameter). ^(c) Single sample, average of 50measurements. ^(d) By the 4 × V_(Total)/σmethod. For the first number,V_(Total) was calculated by the single-point adsorption method; for thenumber in brackets V_(Total) was calculated via V_(Total) = (1/ρ_(b)) −(1/ρ_(s)). ^(e) Calculated via r = 3/ρ_(s)σ.

TABLE 21 Selected Properties of PUA aerogels prepared with Desmodur REtriisocyanate using the middle water and triethylamine (Et₃N)formulations, that is 3.0 mol equivalents of water and 0.6% w/wtriethylamine (refer to Table 11). [RE] bulk skeletal porosity, BETsurface average particle in sol diameter shrinkage density, density, II(% void area, σ pore diameter radius, (M) (cm) ^(a) (%) ^(a, b) ρ_(b) (gcm⁻³) ^(a) ρ_(s) (g cm⁻³) ^(c) space) (m² g⁻¹) (nm) ^(d) r (nm) ^(e)0.0284 1.29 ± 0.01   13 ± 0.64 0.023 ± 0.002 1.24 ± 0.14 98.1 222.4 12[11.8] 10.8 0.0563 1.21 ± 0.04 18.5 ± 2.7 0.037 ± 0.003 1.30 ± 0.01 97.1320.7 7.6 [8.4] 7.2 0.1099 1.29 ± 0.01 12.8 ± 0.7 0.062 ± 0.005 1.23 ±0.03 95 6.55 7.5 [8.7] 372 0.2101 1.28 ± 0.03 13.3 ± 2.1  0.15 ± 0.021.24 ± 0.23 87.8 6.49 7.75 [7.6] 373 0.3019  1.3 ± 0.6 12.4 ± 0.4  0.18± 0.01 1.24 ± 0.25 85.7 19.9 10.6 [11.2] 122 0.5360 1.31 ± 0.01 12.1 ±0.2  0.25 ± 0.02 1.24 ± 0.28 79.8 3.24 6.6 [7.8] 746 ^(a) Average of 5samples. (Mold diameter: 1.40 cm.) ^(b) Shrinkage = 100 × (samplediameter − mold diameter)/(mold diameter). ^(c) Single sample, averageof 50 measurements. ^(d) By the BJH-desorption method; in brackets:width at half maximum. ^(e) Calculated via r = 3/ρ_(s)σ.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modification, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

1. (canceled)
 2. The method of claim 11, wherein the isocyanate is atriisocyanate or a diisocyanate.
 3. (canceled)
 4. The method of claim11, wherein the trialkylamine is a triethylamine.
 5. The method of claim11, further comprising agitating a mixture of the isocyanate, water andtrialkylamine to form the sol-gel material.
 6. The method of claim 11,wherein manufacturing the polyurea aerogel comprises manufacturing avariable density polyurea aerogel.
 7. The method of claim 1, whereindrying the sol-gel material comprises supercritically drying the sol-gelmaterial.
 8. The method of claim 1, wherein drying the sol-gel materialcomprises subcritically drying the sol-gel material.
 9. The method ofclaim 1, wherein the solvent comprises acetone or DMSO.
 10. (canceled)11. A method of manufacturing a three-dimensional nanostructured networkof polyurea, the method comprising: mixing an isocyanate and water and atrialkylamine in a solvent to form a sol-gel material; and drying thesol-gel material to form the three-dimensional nanostructured network ofpolyurea.
 12. The method of claim 11, wherein drying the sol-gelmaterial comprises supercritically drying the sol-gel material to form apolyurea aerogel, wherein mixing an increasing amount of the isocyanateto form the sol-gel material gives rise to an increasing density in thepolyurea aerogel.
 13. The method of claim 12, wherein mixing adecreasing amount of the isocyanate to form the sol-gel material givesrise to a decreasing density in the polyurea aerogel.
 14. The method ofclaim 11, wherein drying the sol-gel material comprises supercriticallydrying the sol-gel material to form the polyurea aerogel, wherein mixinga decreasing amount of the isocyanate to form the sol-gel material givesrise to an increasingly fibrous morphology in the polyurea aerogel. 15.The method of claim 14, wherein mixing an increasing amount of theisocyanate to form the sol-gel material gives rise to an increasinglyparticulate morphology in the polyurea aerogel.
 16. A fibrous aerogelcomprising: a three dimensional network of nanoparticles includingpolyurea, the three dimensional network having fibrous morphology and adensity of less than about 900 mg/cc.
 17. An insulator, a lightweightstructural material, an impact dampening material comprising the aerogelof claim
 16. 18. The fibrous aerogel of claim 16, wherein the threedimensional network having fibrous morphology has a density of less thanabout 150 mg/cc.
 19. (canceled)
 20. The fibrous aerogel of claim 16,wherein the three dimensional network has a density of greater thanabout 150 mg/cc and exhibits a reduced flammability.
 21. The aerogel ofclaim 20, wherein the three dimensional network has a particulatemorphology.
 22. The method of claim 11, further comprising pyrolyzingthe polyurea aerogel to form the carbon aerogel, wherein drying thesol-gel material comprises supercritical drying. 23-25. (canceled) 26.The method of claim 22, further comprising agitating a mixture of theisocyanate, water and trialkylamine to form the sol-gel material. 27-29.(canceled)
 30. The fibrous aerogel of claim 16, wherein the threedimensional network of nanoparticles has a density of less than about 90mg/cc. 31-46. (canceled)
 47. A method of absorbing a liquid-phasematerial comprising contacting the liquid-phase material with athree-dimensional porous polyurea network.
 48. The method of claim 47wherein the liquid-phase material is oil.
 49. The method of claim 47wherein the three-dimensional porous polyurea network is an aerogel.